JPH0455767A - Static electricity measuring device - Google Patents

Abstract

PURPOSE:To reduce generation of dusts without loss of economy and to improve an accuracy and reliability by periodically varying a distance from a matter to be measured and an electrode, and detecting a displacement current flowing to the electrode. CONSTITUTION:A semiconductor substrate 11 of a matter to be measured is secured on a stage 15, and its rear surface is electrically grounded through the stage 15. An electrode 13 is vertically vibrated by a piezoelectric element 12 of a driving mechanism, and a distance between the electrode 13 and the matter 11 is periodically varied. Thus, if an electrostatic capacity between the electrode 13 and the matter 11 is varied and the surface of the matter 11 is charged, a displacement current flows to the electrode 13. This current is detected by current detecting means 14. Since the current I to be detected is represented by a predetermined formula decided by the potential V of the matter 11, a distance D from the matter 11 to the electrode 13, the capacity C, and the effective area S of the electrode 13, the potential V of the matter 11 can be measured from the current I.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a static electricity meter that measures the potential of a statically charged surface of a semiconductor substrate.

BACKGROUND OF THE INVENTION Due to recent advances in microfabrication technology, semiconductor devices are becoming increasingly highly integrated. As a result, the thickness of the insulating films that make up semiconductor devices is now less than 10 nm, and protecting these thin insulating films from dielectric breakdown caused by static electricity is a major key to maintaining high manufacturing yields. ing. To this end, first of all, it is essential to have a technology that accurately evaluates the charging state of semiconductor substrates during manufacturing processes such as dry processes and wet processes.

A conventional static electricity meter will be described below.

FIG. 2 is a configuration diagram of a conventional electrostatic meter. In Figure 2, 1 is the workpiece, 2 is the chopper, 3 is the electrode,
4 is an ammeter which is a current detection means, 5 is a motor, and 6 is a stage.

The operation of the electrostatic meter configured as described above will be described below.

In the conventional method, the distance between the object to be measured 1 placed on an electrically grounded stage 6 and the electrode 3 is fixed at a predetermined distance, and the electrically grounded chopper 2 is connected to the motor 5.
By rotating the object to be measured 1, a pulsating displacement current is induced in the electrode 3, and this current is detected by the current detection means 4, thereby measuring the potential of the object to be measured 1.

Now, the potential of the object to be measured 1 is V (V), the object to be measured 1 and the electrode 3
The capacitance between the electrodes is C(F), and the effective area of the electrode 3 is S(
Hi), the average distance between the object to be measured 1 and the electrode 3 is D (m)
, the dielectric constant is ε (F/m), the current 1 (A) detected by the current detection means 4 can be expressed by the following equation.

■=Yu=Dan・Length Σ・Sat・■(1) ■= dt dt dt D In this way, the current I is generated because the effective area S of the electrode 3 is changed by the chopper 2. this is chopper 2
If it is a rotary type as shown in the figure, it depends on the number of divisions of the chopper 2 and the rotational speed of the motor 5.

If the measurement conditions are appropriately determined, the values other than V on the right side of the fi1 formula are known quantities, so it is possible to measure the value of the potential V of the object to be measured by detecting the current (2).

Problems to be Solved by the Invention However, the above conventional configuration has the following problems.

First, when using a rotary chopper, there is a mechanical part to drive the chopper, which generates a lot of minute dust. Therefore, it is not suitable for applications such as inspection of semiconductor devices, where the generation of dust adversely affects the manufacturing yield of products.

Furthermore, since the measured value varies depending on the distance and the chopper's rotation speed, the measurement accuracy is significantly lower than that of normal voltage measurement. Normally, the accuracy is on the order of several volts. However, if you use a quartz lock method to control the rotation speed,
Control on the order of ppm is also possible, but the equipment becomes expensive and complicated.

The object of the present invention is to solve the problems of the above-mentioned conventional methods, and to provide a static electricity measuring instrument that generates extremely little dust, has high accuracy, and is highly reliable, without impairing economic efficiency.

Means for Solving the Problems In order to achieve these objects, the present invention includes an electrode having a drive mechanism close to the surface of the object to be measured, and a current detection means for detecting a displacement current flowing through the electrode. There is.

The apparatus also includes an electrode having a drive mechanism close to the surface of the object to be measured, a power supply for applying a variable potential to this electrode, and current detection means for detecting a displacement current flowing through this electrode.

The device also includes an electrode close to the surface of the object to be measured, current detection means for detecting a displacement current flowing through the electrode, and a shielding plate that maintains an airtight space between the object to be measured and the electrode.

Operation The process by which the object of the present invention is achieved by these configurations will be explained in order below.

By periodically changing the distance between the object to be measured and the electrode, the capacitance between the object to be measured and the electrode changes periodically.
If there is a potential difference between the object to be measured and the electrode, a displacement current flows through the electrode. The relationship between this displacement current and the potential of the object to be measured is
Since it is uniquely determined by the amount of change in capacitance, the potential of the object to be measured can be measured from the displacement current.

Since the change in capacitance is proportional to the rate of change of the reciprocal of the distance between the electrode and the object to be measured, if the average distance is made small, a sufficient rate of change in capacitance can be achieved even if the change in distance is small. Therefore,
The drive mechanism can also use a voice coil or a voltage element, and the mechanical part can be significantly simplified. Therefore, compared to the case where a rotary chopper is used, the generation of dust is significantly reduced.

In addition, the measurement accuracy depends on the control accuracy of D,
Since a voice coil and a voltage element can be used, it is easy to control the vibration amplitude of the electrode, and high measurement accuracy can be easily obtained. Moreover, since the structure is simple, reliability is high.

The displacement current flowing through the electrode is proportional to the product of the potential difference between the object to be measured and the power supply output and the rate of change in capacitance between the object to be measured and the electrode. First, the capacitance between the object to be measured and the electrode changes periodically by periodically changing the distance between the object to be measured and the electrode, and then the potential applied to the electrode is changed. Check the voltage at which the displacement current becomes O. When the displacement current is 0, the electrode and the object to be measured are at the same potential, so by reading the power supply voltage at this time, the potential V of the object to be measured can be measured.

Here, although the generation of dust is suppressed and the reliability is high as in the first invention, an additional feature is that the absolute value of capacitance or distance is not required to measure the potential of the object to be measured. is added. In this case, the measurement accuracy mainly depends on the current detection sensitivity for determining the condition where the current is zero. In other words, the larger the capacitance change and the higher the sensitivity of the ammeter that is the current detection means, the better.However, since these values can usually be obtained sufficiently high, the cost is lower than that of the conventional chopper type. High measurement accuracy can be obtained without significantly increasing the value.

The space between the electrode and the object to be measured is kept airtight, and even if some dust is generated due to vibration of the electrode, it will not reach the object to be measured, allowing extremely normal measurements.

It is also possible to reduce the pressure in the airtight area, which prevents vibrations from propagating as sound waves and causing dust.

Examples Examples of the first invention, second invention, and third invention are as follows:
Each will be explained with reference to the drawings.

FIGS. 1(A) to 1(C) are configuration diagrams of static electricity measuring instruments in an embodiment of the first invention, an embodiment of the second invention, and an embodiment of the third invention, respectively.

In FIGS. 1(A) to (C), 11 is a semiconductor substrate which is an object to be measured, 12 is a piezoelectric element which is a driving mechanism, 13 is an electrode, 14 is an ammeter which is a current detection means, and 15 is grounded. 16 is an electrostatic shield, 17 is a power source, and 18 is a dielectric film serving as a shielding plate.

The operation of the apparatus shown in FIG. 1A, which is an embodiment of the first invention, will be described below.

A semiconductor substrate 11, which is an object to be measured, is fixed on a stage 15, and its back surface is electrically grounded via the stage 15. Piezoelectric element 12 whose electrode 13 is a driving mechanism
The distance between the electrode 13 and the object to be measured 11 changes periodically. The piezoelectric element 12 and the electrode 13 are connected by an arm of an appropriate length.
The vibration of the piezoelectric element is magnified by the lever principle. This changes the capacitance between the electrode 13 and the object to be measured 11, and if the surface of the object to be measured 11 is charged, a displacement current flows through the electrode 13. This is the current detection means 1
Detected by 4. The detected current 1 (A) is determined by the potential of the object to be measured 11 being V (V), the distance between the object to be measured 11 and the electrode 13 being D (m), the capacitance C (F), and the electrode 13 The effective area of s crrt is expressed by the following formula.

I=dQ=dC, v-d(1/D), εs■ (2゜d
t dt di Here, in the right side of equation (2), everything other than ■ can be known, so the potential V of the object to be measured 11 can be measured from the current ■.

In this method, the change in capacitance C is the difference between the electrode 13 and the object to be measured 11.
It is proportional to the rate of change of the reciprocal of the distance between Now, by setting the average amount of distance to be sufficiently small, around 1 (I), the amount of change in distance can be as small as, for example, 0.5 (+on). As in this embodiment, if the electrode 13 is driven by the piezoelectric element 12, which is a drive mechanism, on the principle of leverage, a sufficient stroke can be obtained, and the mechanical part can be significantly simplified. Therefore, in addition to being economical, the generation of dust is significantly reduced.

Furthermore, the accuracy of measurement mainly depends on the control accuracy of D, but since the piezoelectric element 12 is used, the electrode 13
It is also easy to control the vibration amplitude, and high measurement accuracy can be obtained. Further, the electrostatic shield 16 made of a conductor is connected to the electrode 13.
This prevents a displacement current from flowing between the device and the object other than the object to be measured 11, thereby preventing a decrease in measurement accuracy. In this example, 1
We obtained a measurement accuracy of 7 or more, which is about an order of magnitude more accurate than the conventional chopper type at the same cost. Since the structure is extremely simple as described above, the reliability is also high.

In this example, the average value of the distance was set to around 1 (n+n), and the amount of change in distance was set to 0.5 (ran), but this is due to the mechanical accuracy that can be achieved or the amount required for measurement. There is no problem in changing it depending on the accuracy.

The operation of the apparatus shown in FIG. 1B, which is an embodiment of the second invention, will be described below.

The second embodiment is the same as the first embodiment except that it includes a power source 17 that makes the potential of the electrode 13 variable, so that the current 1 (A) flowing through the electrode 13 is
, the potential given to the electrode 13 by the power source 17 is v' (v), the distance between the object to be measured 11 and the electrode 13 is D (m), the capacitance C (F), the electrode The effective area of 13 is expressed by the following equation as S (nf).

Therefore, at a voltage where the potential V' is changed and the current I becomes 0 (A), the relationship v=v' holds true, and it is possible to measure the potential V of the device under test 11 from the power supply voltage at this time. can.

The second embodiment is similar to the first embodiment in that dust generation is suppressed and reliability is high, but in addition, (3
) As can be seen from the equation, a new feature is added to the measurement of the potential (2) of the object to be measured 11 in that the absolute values of the capacitance C, distance, effective surface 8IS, etc. are not required.

The measurement accuracy depends on the detection sensitivity for determining the voltage of the power supply 17 at which the current becomes zero. In other words, the larger the change in capacitance C and the higher the sensitivity of the current detection means 14, the better; however, these values can usually be obtained sufficiently high, so high measurement accuracy can be easily obtained. A new effect is born. For example, using a power supply with an accuracy of about IQmV and an AC ammeter with a measurement accuracy of about 1 nA,
Assuming that the amount of change in capacitance is 1 pF and the period of change is 1 kHz,
A measurement accuracy of about 10 QmV can be obtained. In this way, accuracy can be improved by approximately two orders of magnitude at the same cost compared to the conventional chopper type.

Although the potential of the electrode 13 is changed from the ground potential by the power source 17, it goes without saying that the potential of the stage 15 may be changed instead.

The operation of the apparatus shown in FIG. 1C, which is an embodiment of the third invention, will be described below.

In the third embodiment, the electrode 13 and its drive mechanism 12 are surrounded by a shielding plate 18 made of quartz and an electrostatic shielding 16 made of a conductive material, which protects the object to be measured 11 from the second embodiment. A new function to keep it airtight has been added. As a result, the electrode 13
Alternatively, there is a feature that the dust generated by the drive mechanism 12 does not reach the object to be measured 11. Furthermore, in this embodiment, the interior surrounded by the shielding plate 18 and the electrostatic shielding 16 is in a reduced pressure state, and the transmission of vibrations due to the propagation of sound waves is suppressed, so that the generation of dust is extremely small. Furthermore, by using a dielectric material with a high dielectric constant for the shielding plate 18, the capacitance between the electrode 13 and the object to be measured 11 increases, resulting in an effect of improving sensitivity.

In this embodiment, the pressure around the electrode 11 is reduced, but it goes without saying that the pressure may be set to normal pressure.

Moreover, although the material of the shielding plate 18 is quartz, it goes without saying that it may be made of various resins or inorganic materials. Further, since the diffusion of dust is blocked by the shielding plate 11, it goes without saying that a rotary drive mechanism or a single chopper type as described in the conventional example may be employed.

In addition, in the first invention, second invention, and third invention described above, a piezoelectric element is used as the drive mechanism 12 for vibrating the electrode 13, but it goes without saying that this may also be a voice coil or the like. .

Further, in the first invention, second invention, and third invention, the case where the object to be measured 11 is fixed upward by the stage has been shown, but this can be changed to any arbitrary position in order to reduce the falling of dust. Needless to say, it is good to change direction.

Furthermore, in the first, second, and third inventions, the object to be measured 11 is a semiconductor substrate, but it goes without saying that it may be made of something other than a semiconductor.

Effects of the Invention As described above, the present invention provides a static electricity measuring instrument that generates very little dust and is highly accurate and reliable.

[Brief explanation of the drawing]

FIGS. 1A to 1C are block diagrams of a static electricity meter according to an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional static electricity meter. 11...Object to be measured, 12...Drive mechanism, 13...Electrode, 14...Current detection means, 17...Power source, 18... Shielding plate. Name of agent: Patent attorney Shigetaka Awano Haka 1 person! ! ...
1 word yz...straight board

Claims (3)

[Claims] (1) A static electricity measuring instrument comprising an electrode having a drive mechanism close to the surface of an object to be measured, and a current detection means for detecting a displacement current flowing through the electrode. (2) An electrostatic meter comprising an electrode having a drive mechanism close to the surface of an object to be measured, a power supply that applies a variable potential to the electrode, and current detection means for detecting a displacement current flowing through the electrode. (3) The electrostatic meter according to claim 2, further comprising a shielding plate that maintains airtightness between the object to be measured and the electrode.